Investigation of Trunk Muscle Size and Function in Older Adults With Chronic Low Back Pain: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Investigation of Trunk Muscle Size and Function in Older Adults With Chronic Low Back Pain (NCT01221233), a randomized na study. The primary outcome is Difference in Percent Change From Baseline in L4 Paraspinal Cross-Sectional Area Asymmetry at 6 Weeks Between Intervention Arms.

2. Clinical Question

The question concerns a measured change in muscle asymmetry, not pain relief, physical function, or another patient-reported outcome. The registry describes rehabilitative ultrasound imaging as a way to assess muscle size and function. It gives context for studying trunk-muscle adaptations in older adults with low back pain, while noting that the impact of NMES on back muscles had been relatively unexplored.

The comparison isolates the difference between the two assigned treatment packages only in the context of the trial as conducted. Since stabilization exercises were included in both arms, the outcome does not compare stabilization exercises with no exercises. Nor does it isolate NMES alone from the effects of the other treatment components. The registry record does not report whether participants or assessors were masked, beyond identifying the trial as having no masking.

3. Trial Design

The registry identifies this as a randomized, unmasked, parallel-group trial, with an enrollment of 38. One arm received NMES with lumbar stabilization exercises; the other received moist heat with lumbar stabilization exercises. The record lists the phase as NA and the status as completed. The stated study dates run from 2011-02-14 to 2011-11-22.

The primary outcome was assessed at baseline and six weeks. Its population description says analyses were completed only on participants who completed the randomized clinical trial. The posted arm summaries report 15 participants for NMES plus stabilization and 19 for moist heat plus stabilization. These are the reported primary-outcome group sizes; they should not be treated as a complete account of enrollment or participant flow.

The adverse-event record gives different at-risk counts: 18 in the NMES arm and 20 in the moist-heat arm. These safety denominators describe the adverse-event summaries and are not interchangeable with the primary-outcome analysis counts. The registry record does not report a participant-flow explanation for the differences in denominators.

The registry record does not report the randomization sequence method, allocation concealment, treatment adherence, or the details of any protocol deviations. It identifies the University of Delaware as sponsor. No additional outcome measures or analyses are posted in the record beyond the one primary outcome measure and one analysis listed.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Analyses were only completed on participants who completed the randomized clinical trial.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Difference in Percent Change From Baseline in L4 Paraspinal Cross-Sectional Area Asymmetry at 6 Weeks Between Intervention Arms, measured over Baseline and 6 Weeks.

The primary endpoint is the difference between arms in percent change from baseline to six weeks in L4 paraspinal cross-sectional area asymmetry. Cross-sectional area is a measure of muscle size, and asymmetry refers to the difference between the right and left sides. The registry describes this outcome as a way to assess a trunk-muscle adaptation using ultrasound imaging.

For each participant, the registry says percent change was calculated as (baseline-6 weeks)/baseline X100%. The resulting participant-level changes were then compared between arms. The NMES-plus-stabilization arm had a reported median of 0.0, with an inter-quartile range from -57.1 to 104.3. The moist-heat-plus-stabilization arm had a median of -17.6, with an inter-quartile range from -51.1 to 250.0.

Using percent change expresses the measured change relative to the participant’s baseline value. The endpoint is used to describe change in the measured asymmetry, not to directly measure pain or everyday function. A change in this imaging measure cannot, by itself, establish how a participant felt or functioned. The registry record does not report a threshold for what would count as an important change in this outcome.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary analysis concerns a continuous outcome expressed as participant-level percent change. The registry states that the calculation used baseline and six-week measurements and that the resulting values were compared between arms using a Mann–Whitney U test because the data did not meet parametric assumptions. The posted analysis names the method as Wilcoxon (Mann–Whitney).

Why compare distributions with a Mann–Whitney test?

In general, the Mann–Whitney test is a rank-based method for comparing observations from two independent groups. It evaluates how values in one group are positioned relative to values in the other, rather than relying on the same assumptions used by a two-sample test of means. It can be useful when the data do not meet the assumptions the investigators considered necessary for a parametric analysis. The registry specifically gives failure to meet parametric assumptions as the reason for using this test.

In general, a rank-based test is not automatically a test of medians in every setting. Its interpretation depends on the shapes and spread of the group distributions as well as their locations. The posted summaries are medians and inter-quartile ranges, while the analysis is labelled as a median difference in final values. The registry record does not report further distributional diagnostics or an explanation of how the test result was translated into that parameter.

What do the median and inter-quartile range convey?

In general, the median is the middle value after observations are ordered. It is less sensitive to extreme observations than the arithmetic mean. The inter-quartile range describes the interval from the lower to the upper quartile and therefore gives information about the spread of the central part of the data. It is not a confidence interval for the median or for the difference between arms.

Here, the arm medians are 0.0 and -17.6. Their inter-quartile ranges are -57.1 to 104.3 and -51.1 to 250.0. The broad ranges show that the reported participant-level changes were dispersed. They cannot establish whether a particular participant changed in a particular way, and they do not by themselves quantify the uncertainty in an arm-to-arm effect.

What does the p-value say?

In general, a p-value describes how compatible the observed test result is with a specified null model, under the assumptions of the test. It is not the probability that the null hypothesis is true, nor is it a measure of the size or clinical importance of an effect. The registry reports p = 1.000 for its Mann–Whitney analysis. Without a confidence interval or fuller inferential output, the record gives limited information about the precision of the between-arm comparison.

A confidence interval, in general, gives a range of effect estimates compatible with the data and the stated method at a specified confidence level. It can help distinguish an imprecise estimate from one that rules out a range of effects. A confidence interval for the reported comparison is not reported in the registry record. The interval summaries for each arm are inter-quartile ranges, not substitutes for such an interval.

Why can over-dispersion matter?

In general, over-dispersion means that observed variability is greater than a statistical model assumes. When a model underestimates variability, its standard errors and uncertainty assessments can be too optimistic. The posted primary analysis is rank-based, and the registry does not report an over-dispersion assessment. The broad inter-quartile ranges demonstrate variability in the summaries but do not, by themselves, establish a particular model problem.

The sample-size assumptions describe planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such calculations are illustrations of the participant counts that a hypothetical design might require under those assumptions; they are not observed power and do not establish the adequacy of this trial’s design. The registry record does not report the trial’s own sample-size justification, the effect used for its original planning, or an original power calculation.

The registry record does not report an interim analysis plan, a prespecified analysis protocol, or details of any adjustment for multiple testing. The posted record includes one primary outcome and one analysis, but that fact does not establish what was prespecified or how multiplicity was handled. These omissions limit what can be inferred about the analysis plan beyond the method and outcome description recorded.

10. Analyses Reported by the Sponsor

The registry reports the sponsor’s analysis as Wilcoxon (Mann–Whitney), with a median difference in final values of 17.6 and p = 1.000. No confidence interval is reported for this analysis. The primary outcome description says participant-level percent changes were compared between arms; the reported analysis label refers to a median difference in final values. The registry record does not provide more detail to reconcile those descriptions.

A separate recalculation of the two-arm comparison is not estimable from the posted summary values. The arm summaries provide medians and inter-quartile ranges, but not the individual observations or the additional information needed to reproduce the Mann–Whitney test. The sponsor’s own analysis is therefore the available inferential result, and no recalculated test should be substituted for it.

The sponsor-reported p-value does not establish that the arms are equivalent. It should be read alongside the arm summaries and the limits of the registry report, including the absence of a confidence interval for the comparison. The record does not report a formal equivalence or non-inferiority analysis.

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome measure and one reported analysis. It does not report secondary posted outcomes. This limits the visible set of results, but does not establish how many outcomes or analyses were considered during study planning or conduct. The registry record does not report a multiplicity adjustment, a hierarchy of outcomes, or a prespecified statistical analysis plan.

In general, when many outcomes, time points, subgroups, or analytic choices are examined, the chance of at least one apparently unusual result can increase unless the analysis plan accounts for those choices. This is the general reason multiplicity matters. The posted record is not sufficient to determine whether such choices arose or whether any adjustment was planned or used.

The primary outcome population is described as participants who completed the randomized clinical trial. The primary analysis group sizes are 15 for NMES with stabilization and 19 for moist heat with stabilization. Adverse-event at-risk counts are 18 and 20, respectively. The record does not give a participant-flow account explaining the differences, nor does it report how missing primary-outcome measurements were handled beyond describing the completer population.

The registry record does not report an intention-to-treat analysis, a missing-data imputation method, sensitivity analyses for missing outcomes, or a comparison of completers with participants who did not complete the trial. It is therefore not possible to assess from the record whether the analyzed participants represent all randomized participants with respect to this outcome. The stated analysis population should be kept distinct from the enrollment total.

The record also does not report interim analyses, stopping rules, or whether investigators had access to accumulating outcome data before the final analysis. These details are not required to interpret the numbers that are posted, but their absence means the analysis process cannot be fully assessed from the registry record.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The adverse-event record reports no serious adverse events among 18 participants at risk in the NMES-plus-stabilization arm and none among 20 at risk in the moist-heat-plus-stabilization arm. It also reports zero deaths in each arm. For other adverse events, the record lists one affected participant among 18 at risk in the NMES arm and zero among 20 at risk in the moist-heat arm. No top serious-event terms are listed.

These are descriptive counts. In general, a count of zero observed events does not show that an event is impossible, and small groups provide limited information about uncommon events. The record does not give further details about the one other adverse event, its severity, timing, or relationship to treatment. It also does not report additional safety analyses.

The adverse-event denominators differ from the primary-outcome analysis counts. The two sets of numbers describe different reported populations and should not be combined or treated as interchangeable. These figures alone do not establish a comparative safety profile.

13. What the Result Does, and Does Not, Mean

The registry results describe percent change in L4 paraspinal cross-sectional area asymmetry from baseline to six weeks among participants who completed the trial. The reported medians were 0.0 for NMES with stabilization and -17.6 for moist heat with stabilization, with broad inter-quartile ranges in both arms. The sponsor’s Mann–Whitney analysis reported a median difference in final values of 17.6 and p = 1.000.

This result does not establish that the treatment packages are equivalent, that they have identical effects, or that one is superior. A non-significant test is not an equivalence test. The record does not report an equivalence margin, a non-inferiority analysis, or a confidence interval for the between-arm comparison. The posted summaries also show substantial spread in participant-level changes, so the group medians do not describe every participant’s outcome.

The endpoint is an ultrasound-based measure of muscle asymmetry. It is not a direct measure of pain, disability, mobility, or quality of life. The registry record does not report results for those outcomes, so this analysis cannot establish whether either treatment package changed them.

The comparison is between two treatment packages, each including lumbar stabilization exercises. It does not isolate the effect of stabilization exercises, nor does it compare NMES with no treatment. Any interpretation must also account for the analysis being restricted to trial completers and the absence of a reported participant-flow explanation.

The result is therefore best understood as a limited statistical description of the recorded endpoint and analysis. It does not provide a basis for medical advice. The registry record does not report a threshold for a clinically important change in asymmetry, and the available analysis does not quantify the uncertainty of the between-arm effect with a confidence interval.

14. Why This Trial Matters Statistically

This trial is statistically notable because it examines an imaging-based measure of trunk-muscle asymmetry in older adults with chronic low back pain. The registry describes ultrasound as a tool for assessing muscle size and function and frames back-muscle adaptation to NMES as relatively unexplored. The primary endpoint turns that question into a measured comparison of participant-level percent change over six weeks.

The design also illustrates the importance of identifying what is actually contrasted. Stabilization exercises were included in both randomized arms; NMES was paired with those exercises in one arm and moist heat with them in the other. The randomized comparison therefore concerns these combined treatment packages, not the separate contribution of every component.

Statistically, the record pairs medians and inter-quartile ranges with a rank-based test, citing failure to meet parametric assumptions. That makes it important to distinguish descriptive summaries from the inferential comparison. The inter-quartile ranges describe spread, while the p-value reports the sponsor’s test result; neither alone provides a confidence interval for the between-arm effect.

The example also highlights why a non-significant result should not be interpreted as proof of equivalence. The analysis reports p = 1.000, but the registry does not report a confidence interval, an equivalence margin, or a formal equivalence design. Sample-size planning illustrations based on an observed effect are not observed power and do not replace the trial’s own planning rationale, which is not reported in the registry record.

Finally, the registry identifies a completer analysis population and separate safety denominators, but does not explain participant flow or missing-data handling. Those details matter when assessing how far a result can be generalized from the analyzed participants to everyone randomized.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The primary-outcome analysis is described as restricted to participants who completed the randomized clinical trial. The registry record does not explain why the primary-outcome counts differ from enrollment, provide a participant-flow account, or report the handling of missing measurements. This leaves uncertainty about how the analyzed group relates to all randomized participants.

The posted primary outcome is an imaging measure of asymmetry, not a direct report of symptoms or function. No other outcome measures are posted, so the record does not show whether the observed muscle-size measure corresponded to changes in other aspects of health. A threshold for a clinically important change is not reported in the registry record.

The endpoint summaries are medians and inter-quartile ranges, and the reported test has a p-value but no confidence interval. The inter-quartile ranges are broad, while the estimate’s precision cannot be assessed from a confidence interval in the posted analysis. The record does not provide individual data that would permit an independent reconstruction of the rank-based test.

The record does not report the randomization method, allocation concealment, adherence, protocol deviations, or detailed masking procedures beyond identifying the trial as unmasked. It also does not report a statistical analysis plan, sample-size justification, interim analysis plan, or multiplicity handling. These omissions limit assessment of design and analysis decisions.

The trial compares two packages that both include stabilization exercises. The result cannot isolate the contribution of NMES, moist heat, or stabilization exercises individually. The safety summaries are descriptive and include limited event detail; the record does not report the nature or treatment relationship of the one other adverse event.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Investigation of Trunk Muscle Size and Function in Older Adults With Chronic Low Back Pain — NCT01221233.
• Registry record last updated 2019-10-28; status last verified 2019-10.
• Results first posted 2019-10-28.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

The registry describes a completed randomized, unmasked, parallel-group trial with an enrollment of 38, sponsored by the University of Delaware. The arms combined NMES or moist heat with lumbar stabilization exercises. The primary endpoint was percent change from baseline to six weeks in L4 paraspinal cross-sectional area asymmetry.

Among trial completers, the reported medians were 0.0 for NMES with stabilization and -17.6 for moist heat with stabilization. The sponsor’s Mann–Whitney analysis reported a median difference in final values of 17.6 and p = 1.000. A confidence interval for that comparison is not reported in the registry record. The analysis does not establish equivalence between the arms.

The primary analysis was limited to completers, and the registry record does not explain participant flow or missing-data handling. Safety summaries report no serious adverse events or deaths in either arm, and one other adverse event in the NMES arm. These counts are descriptive and use different denominators from the primary-outcome analyses.